1. Field of the Invention
The present invention relates to a parking brake for a hydraulic braking systems wherein service brakes are hydraulically applied to effect a brake application in the wheel brakes and resiliently retained in an applied condition without hydraulic pressure until released by a reapplication of hydraulic pressure.
2. Description of the Related Art
It is known to control the brake function of a parking brake through a cable control of a cam or lever to mechanically apply and release a service brake. In addition, electrical control of parking brake systems could also be achieved by a spring apply and a hydraulic or air release using a two-position switch to supply current to activate a solenoid actuated valve. The parking brake being applied by a spring that acts through a linkage to provide a mechanical force that moves friction linings into engagement with a drum or disc brake to effect a parking brake application such as disclosed in shown in U.S. Pat. No. 5,370,449. A solenoid latching mechanism for a parking brake is shown in U.S. Pat. No. 5,443,132 and a hydraulically applied and released parking brake mechanism has been suggested in U.S. Pat. No. 5,161,650. This patented arrangement provides rigid coupling forcing brake friction surfaces into engagement. In addition, it is known to provide for a hydraulic apply, but a spring-loaded release of a parking brake mechanism. Unfortunately in such a spring loaded release design it could be susceptible to an unintended release in cases where the clamp load of the brake caliper might be reduced and as a result the cam could move to the released position under the force of the release spring. This would cause the parking brake to release unintentionally.
It is desirable to provide a certain amount of compliance or resilience to a parking brake assembly to avoid brake release or undue strain on the braking system due to dimensional variations in the brake mechanism as might, for example, be caused by temperature induced expansion or contraction of brake mechanism components.